His smooth swing sent singles and doubles skittering through gaps in the defense, but even at cozy Wrigley Field from 1986 to 1988, he only occasionally drove balls over the fence.

Palmeiro added pop when he reached Texas in 1989, but he was still no slugger ... until 1993. That year, he leaped to 37 home runs, from 22 the season before. And he never looked back, hitting 38 or more home runs in nine of the next 10 seasons.

Fans assumed Palmeiro's career progression was normal - a talented young hitter growing into his body. But with the revelation Monday that Palmeiro had tested positive for a performance enhancer, his evolution is suddenly in question.

Could a hitter suddenly transform so completely on his own? Are steroids a likely culprit in such a long and successful career? If he was using them all along, why did he never develop a hulking physique?

Doctors and baseball observers disagree on the answers to these questions. Some say it couldn't be clearer that steroids help players. Others say the impact of such drugs is almost as much a mystery today as it was 10 years ago.

Dr. William Howard, a surgeon specializing in sports medicine at Union Memorial Hospital, said steroids do not turn pedestrian athletes into pros but unquestionably turn pros into stars and superstars.

"Steroids do not help you hit the curveball," he said. "What they do is help build muscle, and what that does is allow you to swing the bat faster. All these guys in the majors can hit the ball. That's how they got there. What they're looking for is that little boost to make the ball go 10 or 15 feet farther."

Steroids aren't magical, agreed Dr. Charles E. Yesalis, a Penn State epidemiologist who studies sports doping, but they add the extra reaction time that can make a good player great.

"When you have something that increases performance in a highly competitive field by half of 1 percent, that's huge," Yesalis said.

The assessments by Howard and Yesalis jibe with the observations of former players who admitted using steroids.

"That's the way I felt, like I could just try to meet the ball and - wham! - it's going to go 1,000 mph," the late Ken Caminiti told Sports Illustrated in 2002. "Man, I felt good. I'd think, damn, this pitcher's in trouble, and I'd crush the ball 450 feet with almost no effort. It's all about getting an edge."

Caminiti grew markedly more muscular and emerged as a power hitter in the middle of a career he had started as a line-drive hitter. Caminiti died of a drug overdose last year.

Despite such empirical examples, many observers are frustrated by the absence of definitive studies on performance enhancers in baseball. Such studies would be hard to perform, because steroids are illegal and Major League Baseball is trying to eradicate, not research, them.

Researchers have been frustrated even in attempts to measure bat speeds to see if they have increased over time.

Will Carroll writes regularly about sports medicine and authored The Juice: The Real Story of Baseball's Drug Problems.

He said he started working on the book because readers often asked him about steroids and he didn't have many concrete answers. More than a year of researching later, he said he still doesn't have many.

"Baseball is a very complex sport," he said. "We know steroids make you bigger, we know they make you stronger, we know they make you faster, but we don't know if they improve your baseball skills."

Carroll's argument is common among those less certain about the use of steroids in baseball. Such drugs have obvious benefits for sprinters or offensive tackles but have a less definite impact on anything involving coordination, their argument goes.

Carroll cited an Auburn University study that found forearm strength did not equate to hitting power. But, he added, such studies might lose relevance when examining major league players, who are by definition exceptional athletes and are separated by the thinnest advantages in reflexes or confidence.

Carroll said that users such as Caminiti and Jason Giambi (whose revelation was made in grand jury testimony leaked to the San Francisco Chronicle) probably benefited from taking drugs but said he has no idea how much.

Many scratched their heads when Jose Canseco said he had injected Palmeiro with steroids when the two were teammates in the early 1990s. Palmeiro jabbed his finger in the air as he denied Canseco's charges at congressional hearings in March. Fans and lawmakers alike deemed his indignity credible.

Palmeiro had never seemed a classic steroid case. He's not unusually bulky for a ballplayer; he's known more for smoothness than hitting tape-measure home runs; he has been preternaturally consistent; and he has never experienced the nagging pulls and strains associated with hulking sluggers.

But the effects of performance enhancers can be subtle, experts said.

"Taken in small amounts, they help you heal," said Howard, noting that Palmeiro has been uncommonly durable throughout his career. "It's only when you take them in larger amounts and hit the weights that you get too strong for your joints and start to get injured more."

The fact that Palmeiro was never a hulk also doesn't mean much, researchers said. He could have injected the drugs for years without growing if he never lifted weights vigorously.

"Was he taking something? Probably," Carroll said. "Was he taking it over a long time? Probably. But was he getting any effect? We don't know. The idea that you can pick out steroid users by appearance is laughable."

Palmeiro's power spiked shortly after Canseco became a teammate and, according to Canseco's book, introduced Palmeiro to steroids.

This season, Palmeiro started slowly, but his average began to climb in May, just after he reportedly tested positive. Researchers are reluctant to link such short-term performance swings to drug use, saying random chance is the more likely explanation.

Palmeiro's career progression is unusual but not unprecedented. Most big-time sluggers start hitting home runs early, but many players add power as they mature.

Stan Musial was a slashing line-drive hitter who never hit more than 19 homers in a season before he was 27 but ended up with 475. Carl Yastrzemski followed a similar track, never hitting more than 20 homers before he turned 27 but drilling 44 that year and finishing with 452.

Palmeiro had his first big power season at 28 and has 569 homers, eighth all-time.